/**
 * @Author sy
 * @Date 2022/9/13
 */
public class Expe4T4 {
    public static void main(String[] args) {
        Long sum = 0L;
        Long num = 1L;
        for (int i = 1 ;i <= 20;i++){
            for (int j = 1; j <= 20;j++){
                num = num * j;
            }
            sum += num;
        }
        System.out.println(sum);
    }
}
